This invention relates to an illumination compensation device of a scanner for balancing the light intensity on every pixel of the optic-electric image sensor of the scanner to provide higher scanning quality.
Optic-electric image sensors, such as CCD (Charge-Coupled Device) and CIS (Contact Image Sensor), possess the capability transferring light intensity to electric signal. Hence, they have been broadly used in many fields. Scanner and fax machines are the known cases. In the U.S. Pat. No. 5,115,374, a build-in scanner of a computer was disclosed. The conventional light source of a scanner is a straight cylindrical lamp tube. The illumination at the middle portion of the conventional light source is always higher than that at both ends. Hence, when a picture or document sheet is scanned, the unbalanced illumination of the conventional light source causes the scanned image to be distorted and dimmed at its margins. In order to resolve the above problem of a scanner, one disclosed method provides elongating the lamp tube of the scanner. This method can not efficiently resolve the above problems, and the size of the scanner is also enlarged.
In the U.S. Pat. No. 08/768,663 of the applicants, an illumination compensation device of a scanner had been provided to resolve the above problems of a scanner. The illumination compensation device includes at least one bent light source, where the bent light source is a cylindrical lamp tube with a straight middle portion and two bent ends. The bent light source can balance the illumination on the whole scanning line without elongating its width. However, unequal light intensity is caused on the optic-electric sensor of the scanner of the prior art. It is noted that, with the same illumination on the object plane of a lens, the light intensity at the margin of the image plane of the lens is smaller than the image plane's middle portion. Although the scanning quality of a scanner with the bent light source is better than that with the elongated light source described above, the straight middle portion of the bent light source of the prior art still causes non-uniform light intensity on the scanning line.
Besides, in order to prevent the power wires of the light source disturbing the scanning operation of the scanner, the power wires are usually together connected to the power supply from one side of the light source. Since the power wires of the bent light source of the prior art, as shown in FIG. 1 and FIG. 2, are needed to be bent at a large angle or multiple times, the power wires are easily damaged.